Biofuels - the technology, where to use and funding mechanismsNovember 2008

Biofuels. The one word to strike fear into design teams driven down the wood-burning route by renewables obligations. But is it really that difficult? In the first of a two-part article (see part two), BSRIA explains the technology, where it can be used, and what funding mechanisms are available.

Tighter regulations for new homes and businesses, new energy assessment methods and demand for renewable energy buildings will keep the construction industry very busy. The International Energy Agency (IEA) forecasts, on the basis of present policies, that global energy demand will be more than 50 percent higher in 2030 than today. On 23 January 2008, the EC published a Directive on how a 20 percent renewable target should be tackled. The UK's current target is 15 percent.

The most obvious, green and environmentally-friendly source of fuel grows around us: biomass. Wood coppice, mature bark, crop and wood residues can all be burned in large or small units, known generically as wood-chip boilers.

But is this the right way for the UK to reduce its carbon emissions? Do biomass heating systems save the most carbon with the highest cost-effectiveness compared to wind, solar or hydro power?

Security of supply

According to DEFRA sources, around 12 percent of the UK's land is composed of forests and other woodland. The UK Biomass Strategy includes a target to manage this resource and create business opportunities for farms and the general rural economy. Such policies are crucial for creating a secure and sustainable supply network for domestic biomass.

The EU Agriculture and Rural Development Institute has estimated that 27 percent of the biomass resource could come from agricultural crops, with 15 percent imported into the EU. Forestry residues, other woody biomass and waste would provide the remainder.

That said, the EU is already grappling with the consequences of a rapid growth in the demand for biofuels, which is stressing the world's land and water resources at a time when demand for food and forest products is also increasing.

The right choice

A 400 kW district-heating biomass bolierWood burning devices fall into one of two types: domestic stoves and boilers and commercial wood-burning furnaces. The most common and convenient systems for private housing are pellet boilers in the size range of 15 - 50 kWth. These are systems that are easy to run with very little maintenance. They are also easy to combine with solar panels and buffer tanks.

Medium-sized plants (200 kWth - 10MWth), perhaps burning wood chips and mature wood from forestry, represent the most common and economic systems for district heating projects, offices, hotels and similar buildings.

Large-scale plants greater than 10 MWth tend to burn straw, wood and organic waste. Such systems are often combined with a CHP unit and are suitable for serving large district heating schemes or for providing industrial process heat.

Operational issues

While wood-chip prices are economic and attractive, the operational characteristics of wood-burning systems are very different from those of gas or oil. Differences between the fuels, the quality of the fuel, and major technical differences of the combustion process require specifiers and users alike to have a much greater understanding of biomass boiler operation.

Although larger biomass boilers cannot be controlled in the same manner as gas or oil-based systems, (pellet-systems are more responsive), leading boiler manufacturers are beginning to introduce new controls that enable characteristics of the burning process to be visualised on a computer.

An example of a biomass boiler with an integral fuel-delivery system. Austrian-made products are now being imported to the UK by mainstream boiler suppliers.
Image courtesy Kohlbach Gmbh (click image to zoom)Monitoring technology also enables thorough data collection, such as exhaust temperature and composition, rest-oxygen linked with the supply air, combustion chamber temperature and hydraulic aggregates. Control systems are available to link with back-up gas or oil-fired boilers.

Monitoring data enables a boiler manager to fine-tune and optimise the behaviour of a biomass boiler depending on loads, the weather or changes in the type of fuel. Data can also be mined for energy reports.

Purchasing most of the key boiler components (including the controls) from a single supplier can deliver clear advantages, not only in product sourcing, installation and commissioning, but also in having a single point of contact. That person' s task will be to lead the entire process from initial briefing through to design, construction and initial operation, preferably with a period of fine-tuning to match the boiler's operating characteristics to the users' requirements.

Only the boiler manufacturer will have in-depth knowledge of the product, and the one most likely to understand any faults and reduce downtime.

A specialist supplier should not present a standard load and exhaust test report to a potential client. They should be able to demonstrate the performance of their system by reference to similar projects, using similar boiler plant, fuel composition and emission characteristics.

Funding mechanisms

Funding for biomass boilers is available from DEFRA (click here for details). A five-year biomass capital-grant scheme was announced in 2006 in the Climate Change Programme Review. The aim of this scheme is to support the installation of biomass-fuelled heating and combined heat and power projects in the industrial, commercial and community sectors in England.

Capital grants will be awarded towards the cost of the heat or combined heat and power equipment. There will be a variable rate up to a maximum of 40% of the difference in cost compared with installation of a fossil-fuel alternative. The minimum grant will be £25,000 and the maximum single award will be £1 million.